One type of polymer electrolyte membrane fuel cell (PEMFC), shown schematically in FIG. 1 of the accompanying diagrammatic drawings, may comprise a thin sheet 2 of a hydrogen-ion conducting Polymer Electrolyte Membrane (PEM) sandwiched on both sides by a layer 4 of platinum catalyst and an electrode 6. The layers 2, 4, 6 make up a Membrane Electrode Assembly (MEA) of less than 1 mm thickness.
In a PEMFC, hydrogen is introduced at the anode (fuel electrode) which results in the following electrochemical reaction:Pt-Anode (Fuel Electrode) 2H2→4H++4e−
The hydrogen ions migrate through the conducting PEM to the cathode. Simultaneously, an oxidant is introduced at the cathode (oxidant electrode) where the following electrochemical reaction takes place:Pt-Cathode (Oxidant Electrode) O2+4H++4e−→2H2O
Thus, electrons and protons are consumed to produce water and heat. Connecting the two electrodes through an external circuit causes an electrical current to flow in the circuit and withdraw electrical power from the cell.
Preferred ion-conducting polymeric materials for use as components of polymer electrolyte membranes in fuel cells have high conductivity (low EW, or high ion-exchange capacities), low water uptake, robustness and solubility in solvents which can be used to cast the membranes. However, some of the aforementioned requirements compete with one another. For example, steps taken to increase solubility of the materials in casting solvents may, disadvantageously, increase the water uptake of the materials; and steps taken to increase the conductivity of the materials will tend also to increase water absorption leading to premature failure of the materials when used in fuel cells.